Sleep should be the great equalizer.Whatever differences might divide us during the day, the nonconsciousness that comes with nighttime should be one thing we all have in common.

It ain't necessarily so. Scientists have now found significant differences exist in how people sleep in the U.S. depending on race, ethnicity and country of origin, suggesting genetic or cultural differences in shut-eye patterns. This line of research could help identify how these disparities might affect health and find better ways to improve sleep.

One study looked at sleep data gathered from more than 430,000 people in the U.S. between 2004 and 2010 as part of the National Health Interview Surveys, which the U.S. Centers for Disease Control and Prevention conducts annually to monitor the country's well-being. They found that foreign-born respondents were generally more likely to sleep the recommended healthy six to eight hours each night as compared with native-born Americans.

"This study is particularly interesting, because it goes to show that the unhealthy American lifestyle includes more than a poor diet and lack of exercise—it also means unhealthy sleep patterns, and this can lead to important health consequences," says sleep researcher Michael Grandner at the University of Pennsylvania, who did not take part in this research. "It seems like foreign-born Americans may be protected by not adopting this unhealthy lifestyle."

Past research suggests that habitually sleeping less or more than the recommended six to eight hours for adults can be linked to certain higher health risks, such as cardiovascular disease, diabetes, obesity, stroke, cancer and accidents as well as instances of mental disorders such as depression. These findings regarding sleep disparities "can help us understand not only who to target for improving sleep with the aim of improving health, but it can help us identify the social and environmental influences on sleep, which might be modifiable," Grandner says. Unlike many other foreign-born persons, African-born Americans were more likely to report sleeping six hours or less, suggesting that helping them find more sleep could help them with other health issues, says the study's lead author Abhishek Pandey, a sleep researcher at the State University of New York Downstate Medical Center.

Another study analyzed 439 volunteers in the Chicago Area Sleep Study, a randomly selected, racially diverse sample of Chicago adults who donned wrist sensors that measured how long they slept each night for a week and answered surveys about sleep quality and daytime drowsiness. Researchers found that white participants on average slept about 30 minutes longer than other ethnic groups whereas blacks reported the worst sleep quality and Asians claimed to be the most sleepy during the day.

These disparities apparently represent normal experiences, and not underlying sleep disorders, says the study's lead author Mercedes Carnethon, an epidemiologist at Northwestern University. For instance, these differences persisted even after statistically adjusting for cardiovascular disease risk factors that researchers already know are linked with poor sleep, such as body mass index, high blood pressure and diabetes. The scientists also excluded people who had evidence of mild to moderate sleep apnea, a disorder that causes abnormal pauses in breathing during sleep.

"These studies show very clearly that when, how and how much you sleep is partially determined by who you are and where you come from," Grandner says. Pandey, Carnethon and their colleagues detailed their findings June 13 at the annual meeting of the Associated Professional Sleep Societies in Boston.

Differences in sleep patterns might stem from genetic and anatomical variations between groups. For instance, past research suggests blacks and whites might sleep differently because of disparities in inflammation responses and that various groups might display distinctive the structure in their airways, influencing how they breathe during sleep, Pandey says.

Grandner notes such biological distinctions are embedded within a context of familial, cultural, neighborhood and other social factors. "It is only when we can come to grips with this multilayered environment that we can understand why different groups of people experience differences in sleep," he says. "If this seems too daunting, just remember that this is the exact sort of work that was recognized as needed for other domains of healthy behavior, such as healthy diet, adequate exercise, decreased alcohol use and decreased smoking."

ABOUT THE AUTHOR(S)

Charles Q. Choi

Charles Q. Choi is a frequent contributor to Scientific American. His work has also appeared in The New York Times, Science, Nature, Wired, and LiveScience, among others. In his spare time, he has traveled to all seven continents.

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